The present invention relates to a novel positive-working photoresist composition used in the photolithographic patterning process for the manufacture of electronic devices or, more particularly, to a positive-working chemical-amplification photoresist composition exhibiting a great change in the solubility in an aqueous alkaline developer solution by exposure to actinic rays and capable of giving a patterned resist layer with high contrast and good pattern resolution and wide focusing depth latitude.
It is a progressive trend in recent years in the manufacturing process of a variety of electronic devices by utilizing a photoresist composition that a photolithographic patterning process capable of giving a patterned resist layer with pattern resolution as fine as 0.25 xcexcm or even finer is rendered to practical application to be in compliance with the increasing demand for semiconductor devices having a higher and higher degree of integration. In this regard, intensive investigations are now under way for the development of a photolithographic patterning process by utilizing KrF excimer laser beams as the actinic rays for exposure of the resist layer with an object to accomplish pattern resolution of 0.15 to 0.22 xcexcm fineness as a next-generation process.
The feasibility of the above mentioned photolithographic process of high pattern resolution naturally depends on the performance of the photoresist composition used therefor. For example, Japanese Patent Kokai 7-209868 and 10-186665 disclose a positive-working chemical-amplification photoresist composition of which the resinous ingredient is a ternary copolymer consisting of hydroxystyrene or hydroxy-xcex1-methyl-styrene units, styrene units and tert-butyl (meth)acrylate units.
As compared with the positive-working photoresist compositions using a resinous ingredient consisting of polyhydroxystyrene substituted for a part of the hydroxyl groups by acid-dissociable solubility-reducing groups, the above mentioned ternary copolymer is advantageous in respect of small film thickness reduction in the unexposed areas by the development treatment with an aqueous alkaline developer solution to give a patterned resist layer having an excellently orthogonal cross sectional profile. This advantageous behavior of the ternary copolymer in development, however, is still far from sufficient in respect of the contrast of patterning, i.e the solubility change in an aqueous alkaline developer solution by exposure to light, when the above mentioned extremely fine pattern resolution of patterning is targeted.
On the other hand, a photoresist composition is proposed in Japanese Patent Kokai 8-101509 by utilizing a homopolymeric resin of a 1-alkylcycloalkyl acrylate or a binary copolymeric resin thereof with hydroxystyrene. The photoresist composition proposed there, however, is defective due to the relatively large film thickness reduction in the unexposed areas by development not to give an excellently patterned resist layer.
Further, Japanese Patent Kokai 9-73173 discloses a positive-working photoresist composition for exposure with ArF excimer laser beams, in which the resinous ingredient is imparted with an increased acid-dissociability by utilizing an acid-dissociable group having an alkyl group substituting the carbon atom at which an ester group and a cyclic hydrocarbon group are bonded together. Japanese Patent Kokai 10-161313 proposes a positive-working photoresist composition for exposure with ArF excimer laser beams imparted with sensitivity improved still more by using an acid-dissociable group having an alkyl group of at least two carbon atoms introduced into a carbon atom similar to the above. These photoresist compositions, however, are not suitable for exposure with KrF excimer laser beams due to the absence of hydroxystyrene units in the resinous ingredient and also have a problem of relatively low resistance against dry etching when the acid-dissociable group is a cyclohexyl group.
The present invention accordingly has an object, in order to overcome the above described disadvantages in the conventional photoresist compositions, to provide a novel positive-working chemical-amplification photoresist composition suitable for exposure with KrF excimer laser beams and capable of giving a resist layer exhibiting a large change in the solubility in an aqueous alkaline developer solution by exposure to light and giving a patterned resist layer having high contrast and high pattern resolution as well as large focusing depth latitude.
Thus, the positive-working chemical-amplification photoresist composition provided by the present invention comprises, as a uniform solution in an organic solvent:
(A) a resinous compound capable of being imparted with an increase in the solubility in an aqueous alkaline solution by interacting with an acid and consisting essentially of (a) hydroxystyrene units or hydroxy-xcex1-methylstyrene units, (b) styrene units and (c) 1-alkylcyclohexyl (meth)acrylate units represented by the general formula 
in which R1 is a hydrogen atom or a methyl group and R2 is an alkyl group having 1 to 5 or, preferably, 2 to 4 carbon atoms in molar fractions of 40 to 80%, 10 to 40% and 2 to 30%, respectively; and
(B) a radiation-sensitive acid-generating agent capable of releasing an acid by irradiation with actinic rays.
It is preferable that the resinous ingredient as the component (A) is a combination of two different resinous compounds each falling within the definition of the component (A) but being different in the molar fractions of the monomeric units (b) and (c).
It is also preferable that the photoresist composition further comprises (C) an aliphatic tertiary amine compound and/or (D) a phosphorus-containing oxoacid or an ester thereof each in a specified amount.
The invention further provides a positive-working chemical-amplification resist composition comprising:
(A) a resinous compound capable of being imparted with an increase in the solubility in an aqueous alkaline solution by interacting with an acid and consisting essentially of (a) hydroxystyrene units or hydroxy-xcex1-methylstyrene units, (b) styrene units and (c) 1-alkylcyclohexyl (meth)acrylate units represented by the general formula 
in which R1 is a hydrogen atom or a methyl group and R2 is an alkyl group having 1 to 5 or, preferably, 2 to 4 carbon atoms; and
(B) a radiation-sensitive acid-generating agent capable of releasing an acid by irradiation with actinic rays, and capable of forming, on a substrate surface, a layer of which the rate of thickness reduction by dissolution at 23xc2x0 C. in a 4.5% by weight aqueous solution of tetramethylammonium hydroxide is in the range from 0.01 to 100 nm per second or, preferably, from 1 to 30 nm per second.